Understanding the Parts of Medicare

Medicare is more complex than most people expect. There are multiple components, private plan alternatives, and a handful of distinctions that carry real financial consequences. Many people approaching retirement assume Medicare works like a single, simple insurance policy; you turn 65, you sign up, and you're covered. The reality is quite different. Medicare is a multi-part system, and the choices you make at enrollment can affect your costs, access to providers, and financial exposure for years to come. Knowing how each piece works will put you in a much better position when enrollment time arrives.

Medicare Parts A, B and D

Parts A and B of Medicare form the foundation of the program, each covering a different side of medical care. Together they're referred to as Original Medicare, and everything else in the system either builds on top of them or replaces them entirely.

Part A covers the hospital side. This includes inpatient stays, some skilled nursing facility care, and certain home health services. Most people who paid Medicare taxes for at least 10 years through their working years won't owe a monthly premium for Part A, which often leads people to assume that services within this portion of Medicare are essentially free. That's not quite right. While the premium may be zero, deductibles and cost-sharing measures still apply. A single hospital stay can trigger a significant deductible, and extended inpatient care beyond certain thresholds introduces additional daily costs. Understanding what Part A covers and what it doesn't is important before assuming you're protected.

Part B covers the outpatient side. Including doctor visits, lab work, preventive screenings, outpatient procedures, and durable medical equipment like wheelchairs or glucose monitors. Unlike Part A, Part B always carries a monthly premium. Part B also has an annual deductible. Once that deductible is met, you're generally responsible for 20% of covered costs (a structure called coinsurance). That 20% might sound manageable on routine visits, but it adds up quickly with specialists, imaging, chemotherapy, or any ongoing treatment. What makes this particularly important to understand is that Original Medicare (Medicare A and B together) has no annual out-of-pocket maximum. There is no ceiling on what you could owe each year. That open-ended exposure is one of the key reasons most people don't stop at Parts A and B alone.

Additional Parts of Medicare

Part D covers prescription medications through private insurers that have been approved by Medicare. Rather than a single federal drug benefit, Part D is offered through dozens of competing plans, each with its own list of covered drugs (called a formulary), its own premium, and its own cost-sharing structure. Two plans available in the same zip code might cover entirely different medications at entirely different price points.

Because of this variation, it pays to review your specific prescriptions against plan formularies before choosing a Part D plan, rather than simply selecting the one with the lowest premium. A plan that costs less per month may charge significantly more for the drugs you actually take.

One of the most important rules in Part D involves timing. You should enroll in Part D when you are first eligible. Delaying without having other qualifying drug coverage, such as coverage through an employer, results in a permanent late enrollment penalty. This penalty is calculated as a percentage of the national base beneficiary premium and is added to your Part D premium for as long as you have that coverage. It doesn't go away after a set period. Enrolling in a Medicare Advantage plan does include part D within it, and by enrolling in a Medicare Advantage plan in a timely manner you will not be susceptible to this penalty.

The Gap in Original Medicare

Here's where a critical issue comes into focus. If you only have Parts A, B, and D, you have insurance but you also have a lot of exposure. You're responsible for your Part A deductible each time you're admitted to the hospital, your Part B deductible each year, as well as that ongoing 20% coinsurance for outpatient services, with no limit on how high those costs can go. A serious illness or injury could result in thousands of dollars in out-of-pocket costs even though you're covered by Medicare. Because of this, most people are well served by adding either a Medicare Advantage plan or a Medicare Supplement plan to help cap that liability. Both approaches address this problem, but they do so in different ways.

Medicare Advantage (Part C): A Replacement for Original Medicare

Medicare Advantage is the most commonly misunderstood part of the program, largely because of how it's marketed. It is not supplemental coverage added on top of Medicare, it is a replacement for it. When you enroll in a Medicare Advantage plan, a private insurer takes over the delivery of your Medicare benefits. Parts A, B, and D are all bundled together into one plan and a private insurance company will oversee delivering and managing your benefits.

If you've had employer-sponsored health insurance or purchased a plan through the marketplace, Medicare Advantage will likely feel familiar. These plans have networks of doctors and hospitals, just as employer plans do. They have deductibles, copays, coinsurance, and an annual out-of-pocket maximum.

Medicare Advantage plans are required to cover at minimum everything Original Medicare covers, but most go further. This is largely what drives the advertising, as most plans include additional benefits for prescription drugs, dental care, vision, hearing, fitness programs, and other services not covered by Original Medicare. Those extras can be valuable, though it's worth reading the details carefully to understand what's included and what's subject to limitations.

On the cost side when you join a Medicare Advantage plan, you'll pay your standard Part B premium, as well as your premium for your advantage plan, though many plans are available at low or no additional cost depending on where you live.

The tradeoff with Medicare Advantage is network. Because these plans operate like managed care plans, you'll generally need to use providers within the plan's network to receive full benefits, and some plans require referrals to see specialists. For people who travel frequently, split time between states, or have strong existing relationships with out-of-network providers, this is worth weighing carefully.

Medicare Supplement (Medigap): Filling the Gaps in Original Medicare

Medigap plans also go by Medicare Supplement plans. Even with different names, these are the same thing. Medigap policies take a fundamentally different approach. Rather than replacing Original Medicare, they add extra coverage to it. A Medigap plan's purpose is to cover the costs that Parts A and B leave unpaid (the deductibles, copayments and, most importantly, they add an out-of-pocket maximum).

Medigap does not expand your medical benefits into new categories. It won't add dental, vision, or hearing coverage, and it doesn't replace any part of Medicare. What it does is make your out-of-pocket costs predictable. Instead of facing a potentially unlimited 20% exposure on your outpatient care, a Medigap plan picks up that tab. Depending on which plan you choose, you may have very little or essentially no cost-sharing beyond your premiums. Because Medigap doesn't include drug coverage, you'll need to purchase a standalone Part D plan separately.

That means if you go the Medigap route, you're managing and paying three separate premiums: Part B, Part D, and your Medigap policy premium. The monthly cost tends to be higher than a Medicare Advantage plan, but the predictability and flexibility are trade-offs many people value, particularly those with significant health needs or those who want the freedom to see any provider who accepts Medicare without worrying about networks.

One point worth knowing clearly: Medicare Advantage and Medigap cannot be used together. They are two separate approaches to coverage, not two things that layer on top of each other. Choosing one means you won't use the other. Depending on your state there can be rules with Medigap regarding pre-existing conditions and guaranteed issue requirements.

When it comes to supplementing your Medicare coverage, these are the two primary routes. Medicare Advantage offers an all-in-one plan with an out-of-pocket maximum, extra benefits, and familiar structure, with the constraint of a provider network. Medigap offers maximum flexibility and predictable costs by wrapping around Original Medicare, with higher premiums and the need for a separate drug plan.

Neither is universally better. The right path depends on your health history, your preferred providers, the medications you take, and how you personally weigh cost certainty against flexibility. Someone who is relatively healthy, comfortable with networks, and looking to minimize monthly premiums may find Medicare Advantage a strong fit. Someone who sees multiple specialists, values the ability to go to any Medicare-accepting provider nationwide, and wants to minimize surprise bills may prefer the Medigap route.

What matters most is that you make this choice deliberately, with a clear understanding of what each option does and doesn't cover, before you need to use it. To find what makes sense for your specific situation, bring these questions to your next advisor meeting or reach out to our team directly.

---

IMPORTANT DISCLOSURES

This post was created with the assistance of AI tools for research and drafting.  It was reviewed, edited, and fact-checked by Camilla Carvalho before publication.  Please verify any critical information.

These materials are provided for general information and educational purposes based upon publicly available information from sources believed to be reliable—we cannot assure the accuracy or completeness of these materials. The information in these materials may change at any time and without notice.

Spire Wealth Management, LLC is a Federally Registered Investment Advisory Firm. Securities offered through an affiliated company, Spire Securities, LLC., a Registered Broker/Dealer and member FINRA/SIPC.